Various prior art proposals exist for estimating a number of occupants in a confined spaces such as, for example, an elevator, store and so on. For example, in International Publication No. WO 97/02474, there is proposed an improved method based on the use of a matrix of pressure contacts for estimating an actual occupied area of floor in a confined space. Pressure contact points are clustered so as to form composite areas of floor which are occupied and a boundary is provided around each of these areas in order to allow for minimum breathing space between adjacent passengers. On this basis, the total occupied area may be estimated. However, such a method still does not give an accurate estimation of the actual number of passengers in the elevator because the footprints of two passengers standing in very close proximity will be so close that they are clustered together and, to all intents and purposes, are treated as a single footprint. This, of course, does not matter when only occupied or free area in a confined space is of interest. However, it is critical when an actual number of occupants is to be estimated.
This having been said, there is a fundamental difference between, on the one hand, the situation where people are static in a confined space and, on the other hand, when people are moving across a confined space so as to effect dynamic contact therewith. In the static case, for example in an elevator car, as more people are confined into the limited space thereof, their feet inevitably are brought into ever closer proximity. Eventually, it becomes impossible to determine whether adjacent pressure contact points belong to the same footprint or to the adjacent footprints of two people standing almost on top of one another. As noted, this does not matter where an estimation of occupied floor space is all that is required, but it clearly militates against an accurate estimation of the number of occupants.
However, in the second, dynamic case, where people are constantly on the move and where they effect only transient contact with the sensor, the likelihood that two different people in close proximity will exert pressure on the sensor simultaneously is so slim as to be safely negligible. This means that, contrary to the static case discussed above, each distinct cluster of pressure points may be identified with a unique instance of a person making his way across the sensor.